The Prod and QA environments are identical in all respects. I haven't experienced any errors; I was just asking a question driven by laziness on my part.. seeing whether I could skip an unnecessary step.
But you bring up a good point. If a human forgets to copy a metadata change in Prod to QA and the script change relies on the existence of that change, the validation step in QA is a good way to catch that before releasing the revision to production. Thanks much.